Oriented Nano-Structure (“ONS”) optical media provide storage capacities/densities which are increased by a factor as high as about 5, relative to the currently available CD, DVD, HD-DVD, etc., optical disc media. Advantageously, such ONS media and systems are backward compatible with the CD, DVD, HD-DVD technologies, and are suitable for use as small form-factor discs such as are currently employed in personal audio/video devices, e.g., Game Boys®, iPODS®, etc.
Referring to FIG. 1, the upper illustration is a plan view of a data track (or recording cell) of a conventionally encoded optical medium, showing a pattern comprised of a plurality of elongated pits (dark areas) formed in the surface of the medium and the corresponding output pattern of a read head or photodetector which is produced by the pattern of pits, wherein tmin indicates the minimum spacing between adjacent pits which limits the maximum data encoding density and reading rate for a given disc rotation speed.
Still referring to FIG. 1, the lower illustration shows the expected output pattern of a read head or photodetector of a multi-states encoded ONS medium, wherein the surface of the medium includes a data track (or recording cell) with a pattern of pits configured as multilevel oriented nano-structures. As is evident from a comparison of these illustrations, and noting that t<tmin, the areal recording density and data rate is significantly increased (i.e., ≧5×) in the multi-states encoded ONS medium by packing more information (i.e., M states) into the recording cell, while advantageously allowing operation with far-field optics similar to those of conventional optical drives.
Adverting to FIG. 2, shown therein are cross-sectional system views and plan views of the encoded surfaces of conventional CD, DVD, Blu-Ray® media, as well as ONS media, along with associated performance characteristics and operating parameters of each of these media types. As before, it is evident that ONS media offer significantly increased areal recording density and data rate vis-à-vis the earlier generations of optical media by virtue of: (1) decreased spacing between adjacent data tracks; (2) the ability to widely vary the angles of the pit walls with respect to the data tracks, hence the encoding information; and (3) the increased pit density along each data track.
ONS technology possesses the potential for becoming significantly more valuable than conventional optical disc technology, since “write once” and/or “re-writable” ONS discs can attain data storage capacities in the 150-1,000 Gbyte range when in a 5.25 in. diameter format and are usable equally well for content delivery (as in the current CD and DVD markets) and archival storage and retrieval applications.
Conventional optical disc data/information recording and storage systems, e.g., employing read-only and writable CD, DVD, etc., media, rely on a structure comprised of elongated pits which extend in a down-track direction and have discrete lengths determined by the corresponding digital signal. The read-back signal is related to optical reflection changes which occur at the leading and trailing edges of the elongated pits.
FIG. 3(A) is a block diagram schematically illustrating the operating principle and layout of a typical optical system 10 utilized for providing a read-back signal corresponding to encoded data/information from conventional CD, DVD, etc. media, wherein: reference numeral 1 indicates a source of an incident beam of optical energy 2, e.g., a laser diode; reference numeral 3 indicates a collimating lens; reference numeral 4 indicates a beam splitting prism; reference numeral 5 indicates a quarter-wave plate; reference numeral 6 indicates an objective lens; reference numeral 7 indicates the optical disc; reference numeral 8 indicates optics for astigmatic focusing; reference numeral 9 indicates a quadrant-type photodetector (shown in more detail in the plan view of FIG. 3(B)); reference numeral 11 indicates output lines from each of the quadrants a, b, c, and d of the photodetector with corresponding output signals Ia, Ib, Ic, Id; reference numeral 12 indicates a suitable amplifier, e.g., a DC coupled amplifier, for processing the output signals from lines 11; and reference numeral 13 indicates an output line from amplifier 12. Reference numeral 2R indicates a beam of optical energy (“return beam”) reflected from the encoded surface of optical disc 7 back to the beam splitting prism 4, whereat it is separated from the incident beam 2 and directed towards focusing optics 8 and photodetector 9.
In contrast with the conventional optical disc technology utilizing an optical system such as shown in FIG. 3, ONS discs utilize angularly oriented and/or width-modulated marks or pits for data/information encoding, and thus output signals from ONS media involve changes or shifts in the polarization angle or state of reflected (“return”) light. However, since the output signal generated by ONS media is different from that of the conventional media, an optical system such as system 10 of FIG. 3 is not optimally designed for resolving changes in angles/orientations of reflected polarized light from the data marks or pits.
Accordingly, there exists a clear need for optical read-out systems designed and configured for optimally resolving changes in angles/orientations of reflected polarized light from the data marks or pits of ONS media.